1. Field of the Invention
The present invention relates to methods of producing hydrocarbons from a subterranean formation using improved well location patterns, and more particularly, but not by way of limitation, to improved inverted six-spot well patterns for secondary and tertiary recovery procedures carried out in subterranean formations.
2. Description of the Prior Art
In producing subterranean hydrocarbon-containing formations through a plurality of wells, it is a general practice to produce one or more production wells in the formation until production therefrom is depleted, whereupon the depleted wells are shut down and production is continued via other production wells in the formation. When the production from all of the production wells in the formation has been depleted, secondary and tertiary recovery operations are carried out to recover hydrocarbons remaining therein.
In planning the drilling of production wells in a field for subsequently carrying out secondary and/or tertiary recovery operations, e.g., gas repressuring and/or water, fire, steam and solvent flooding, well patterns that are geometrically repeatable have been utilized. When the secondary and/or tertiary recovery operations are commenced, fluid is injected into some of the wells to displace hydrocarbons in the subterranean formation to others of the wells. The front or interface between the injection fluid and hydrocarbon fluids in the formation moves from the injection wells toward the production wells, changing shape as it progresses. Due to the lower pressure around the production wells, a portion of the interface tends to accelerate and cusp into the production wells. Breakthrough of the injected fluid occurs when the interface reaches the production wells.
The most commonly heretofore used well pattern for carrying out hydrocarbon recovery operations is a series of five-spot sub-patterns each having four injection wells at the corners of a square and a production well at the center. Inverted five-spot sub-patterns have also been used having an injection well at the center and production wells at the corners. In a series of five-spot sub-patterns, there are as many injection wells as production wells.
Other basic well sub-patterns which have been used are the inverted seven-spot, and the inverted nine-spot. The term "inverted" is used to designate that the injection well is at the center of the sub-pattern with production wells defining the sub-pattern. In some instances the use of a series of inverted five-spot sub-patterns does not provide an adequate number of producing wells surrounding the injection wells, and the use of a series of seven-spot sub-patterns requires the drilling of too many wells which have become much more expensive to drill in recent years.
By the present invention an improved well pattern is provided having a greater number of producing wells surrounding the injection wells than a series of five-spot sub-patterns and requiring fewer wells than a series of seven-spot sub-patterns.